When you start a computer that is running Windows Vista or Windows 7 one or more of your icons do not appear in the notification area in the lower-right corner of the screen. Also, the Volume Control icon, the Network icon and the Power icon may be missing. I have two Windows 7 systems and this is only happening on the 32-bit machine. But it happens reliably on reboot so I have to do this regularly.

You can make them reappear by deleting two subkeys from the registry.

Back up the Registry by creating a restore point.

Go to Start - Run (or Windows-key + R), type in regedit and hit OK.

Navigate to the key HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\TrayNotify.

In the right pane right-click and delete the values IconStreams and PastIconsStream.

Open up the Task Manager (Ctrl + Shift + Esc), go to the Processes tab, select explorer.exe and click End Process for every instance of explorer.exe. Your desktop icons will disappear; don't worry.

Open the Applications tab and click the New Task button at the bottom-right of the window.

In the message box that pops up type in explorer.exe and hit OK.

Explorer.exe will reload, your desktop will be back, and the missing icons should now be back in the Notification Area where they belong.

Now click the up arrow in the Notification Area and click Customize. Set up your icons to your liking.

Open Regedit again. Navigate to the keys noted above in step 3. Right-click on TrayNotify in the left window. Select Export. Name the export file and click Save.

The next time this happens you can simply double-click the .reg file you just saved, allow it to modify the registry, and do steps 5-7 above. Fixing the problem this way means you don't have to re-set the Notification Area Customizations every time you have to do this.

Alternatively, you can use the batch file below. Highlight from rem begin batch file to rem end batch file. Press CTRL+C to copy the text to the clipboard. Open a plain text editor like Notepad. Press CTRL+V to paste the text. Save the file as Reset Notification Icons.bat. The next time this happens run this batch file. It deletes the proper registry keys, kills the explorer.exe processes, and then restarts explorer.exe.